Drop foot occurs when the nerve stimulation from the central nervous system has slowed or lost connection to the tibialis anterior muscle that lifts the foot during walking. This condition occurs for several reasons, some of which are caused by an accident involving the spinal cord, a stroke, neuropathy, a nervous system disease or any nervous system disconnect that causes the loss of nerve to muscle communication. The devastating effects of this condition result in the inability to walk. The drop foot disability can create emotional and financial hardships for the affected person and their family.
There have been many attempts to help a person with the drop foot condition. The most commonly used device is a brace that limits the foot dropping below a predetermined point. Springs and motors also, have been used to lift the foot. Within the past twenty years, researchers have been electrically stimulating the nerve to flex the muscle that lifts the foot. Physical therapists use electrical stimulation to exercise and rehabilitate injured or paralyzed muscles. Electrodes are placed on the skin over the nerve and muscle and a stimulator device sends electrical pulses to the electrodes that stimulate the muscle.
Portable functional electrical stimulus patents date back to 1954 with U.S. Pat. No. 2,737,183 to Graimo. The patient pressed a switch to start and stop the electrical stimulation. In 1963, U.S. Pat. No. 3,083,712 to Keegan taught a device that initiated electrical stimulation by a heel switch placed under the foot. The use of a foot switch requires the patient to wear shoes. While standing or sitting weight must be shifted to the foot, with the foot switch, to prevent false stimulation. The point the stimulation ends is when the foot switch is activated after the foot contacts the walking surface. Tilt switch and foot switch combinations are described in U.S. Pat. No. 4,796,631 to Grigoryer. A biofeedback-activated electromechanical device is described in U.S. Pat. No. 5,112,296 in 1992. Activation of an electric motor to lift the foot was initiated from muscle activity sensing through skin surface electrodes. U.S. Pat. No. 5,643,332 to Stein in 1997 describes a tilt switch mounted in a device placed under the knee. The tilt switch activates the stimulator at a predetermined angle of the leg. Tri-axis motion sensors are used in U.S. Pat. No. 7,369,896 to Gesotti in 2008 to stimulate muscles to improve motion disorders. Stimulation timing is critical for an FES apparatus to be usable. The prior art addresses this timing issue by either using a foot switch, a tilt switch, motion sensors, or any combination of these sensors to initiate the stimulation.
Other prior art that uses a tilt switch to begin and end stimulation, must be set to a predetermined point when the angle of the leg is at the correct position for stimulation. Since the angle for beginning stimulus is preset, the placement of the controller on the leg is critical for proper function and stimulation. Walking on level ground is also another limiting factor. An inclined surface changes the tilt angle and can cause improper stimulation. In some devices, after the stimulation begins the timing is set to end the stimulation, requiring the patient to walk at that preset pace and stride. Any change in motion and stepping cycle causes false stimulation. Prior art that uses a foot switch to control stimulation must be hard wired or use a wireless transmitter that sends a signal to a control unit in order to determine when to start and stop the nerve stimulation. Prior art is complicated to set up, difficult to operate and wear, and expensive for the patient. These devices require extensive training for the clinician and the patient.